LGA1156 forever
Clarkdale drops into the same LGA1156 sockets used with Lynnfield Core i5 and i7 processors. The motherboards are largely interoperable: one may, for instance, install a Core i5-750 in an H57 motherboard and use it, so long as a discrete graphics card is available. Similarly, we installed our Core i5-661 in a P55 board with discrete graphics, and it worked effortlessly. Just don't expect that H57 motherboard's VGA port to do anything when you have a Lynnfield processor installed, and don't expect to make use of a Clarkdale IGP on a P55 board.

The Core i5-661 in its socket

The bare socket

The Core i7-870 (left) and the Core i5-661 (right).

From left to right: Socket AM3, LGA1156, and LGA775 processors

The stock Core i5-661 cooler is a puny thing, but it's still fairly quiet

Key match-ups to watch
We're about to dive into our performance results, but before we do, let's talk about some competitive scenarios for the various CPUs.

The battle at 200 bucks — The star of today's show, the Core i5-661, is priced at $196. That's a lot to ask for dual-core CPU these days, and that price tag puts it into direct competition with the Phenom II X4 965, AMD's fastest processor, and a prior-gen quad-core, the Core 2 Quad Q9400. Now, the Core i5-661 has a much lower TDP than the 125W Phenom II X4 965, but its 87W rating isn't far from the Q9400's 95W TDP. The question is whether the i5-661's quad-threaded performance and nosebleed-inducing 3.6GHz Turbo Boost frequencies are sufficient to justify its price in the presence of some very tough company.

Duel of the duallies — I've also thrown in the top dual-core versions of the Phenom II and Core 2—the X2 550 and the Duo E8600, respectively—to compete against the newcomer. The prices on these products vary quite a bit, but architecturally, we'll be interested to see how Westmere compares.

The value slug-fest — We underclocked our i5-661 to make it perform like a Core i3-540, a $133 Clarkdale that lacks Turbo Boost. That product matches up against the Core 2 Duo E7600 (its $133 predecessor) and a potentially quite compelling rival from AMD, the $122 Athlon II X4 630. This value offering, based on the 45-nm Propus core, lacks any L3 cache, but matches the i3-540 with a 2.8GHz clock speed and four real CPU cores. Can AMD's value quad manage to steal a win against Intel's new hotness?

Incidentally, those match-ups reveal our thinking in processor selection for this review. We've also thrown in the cheapest Core i7-900-series processor, the i7-920, just for comparison's sake.